Telephone set cord



Filed Nov. 27, 1941 FIG 0 m m r A mvmvron By 1.. J. BOWNE r2 2 c m G r Fu r! Patented Nov. 10, 1942 TELEPHONE SET CORD Langford J. Bowne, HowardBeach, N. Y., assignor to Bell Telephone Laboratories, Incorporated, NewYork, N. Y., a corporation of New York Application November 27, 1941,Serial No. 420,635

4 Claims.

This invention relates to telephone transmission systems and, moreparticularly, to flexible cables or cords for so-called operatorstelephone sets comprising a transmitter and a pairof receiver unitsattached to a headband. Such cords usually consist of four conductors,two for means of the transmitter and one of the receiver units and atthe same time monitor, 1. e., listen,

on another line.

When this additional pair of conductors for the monitoring receiver, isincluded in the telephone set cord; thereby increasing the number ofconductors to six, it has been found that under certain degrees ofatmospheric humidity undesirable cross-tall: between the two pairs of receiver conductors and between the transmitter pair and the pairconnected to the monitoring receiver is experienced due to anunavoidable capacity unbalance between the conductors within the cord.

An object? of the present invention is to reduce cross-talk in flexiblecords of the character described.

While the above object might be attained by carrying the monitoring pairof conductors in a separate cord or cable, a single cord is consideredmore desirable and to obtain the desired reduction in cross-talk byelectrostatically shielding the receiver pairs from each other andreducing the capacity unbalance between the transmitter conductors andthe monitoring conductors.

A feature of the invention, whereby the desired result is obtained,resides in the addition of an additional or seventh conductor within thecord winch is connected at both ends to one of the transmitterconductors and in so arranging the several conductors within the cordthat the three transmitter conductors lie in a plane between the tworeceiver pairs to act as an electrostatic shield therebetween, and thata substantially uniform capacity exists between each receiver conductorand the transmitter conductors.

The invention will be understood from the following description and theaccompanying drawing, Fig. 1 of which shows, schematically, an operatorstelephone set, and its. associated cord arranged in accordance with thepresent invention whereby crosstalk between the two receiver pairs ofthe cord is substantially eliminated when the operator is talking ononeline and monitoring on another line at the same time; and Fig. 2shows a cross section of the telephone set cord.

Referring to the drawing, Fig. 1, an operators telephone set OTcomprising a transmitter T and receiver R is shown connectedby,conductors ti, t2 and TI, 1'2, contained in a flexible cable or cord C,to an operators telephone circuit 00 rminating a line Ll whereby two-way-conversation between the operators transmitter-T and the receiver R andthe line Ll may be carried A second line, L2, is also shown connected toanother receiver unit MB of the operators set OT by means of a thirdpair of conductors mrl and m1'2 contained in the cord or cable C wherebythe operator, by means of receiver unit MR, may monitor, i. e., listenon the line L2 whilg talking on line Ll.

In addition to the conductors tl, t2 and TI, 1'2 and mrl and 11112, anextra conductor t3 is also included in the cord C which conductor isshown as terminating at the two ends of the cord and connected at eachend to the transmitter conductor t2.

By referring to Fig. 2 it will be noted that the above conductors areclosely and uniformly arranged within the cord so that they lie in threeparallel planes, one consisting of conductors H and r2, anotherconsisting of conductors mrl and mr2 and the third or intermediate planeincluding the conductors tl, t2 and 153.

From the foregoing it will be noted from the drawing that the threeclosely positioned conductors tl, t2 and t3 lying in a plane betweenconductors Tl, r2 and mrl and mr2 from an effective non-magnetic shieldbetween the two receiver circuits thereby substantially eliminating thepossibility of crosstalk interference between them.

Further, if the transmitter conductors tl, t2 and t3 and the monitoringreceiver conductors mrl and mri! are all uniformly spaced with respectto each other, the capacity unbalance between either side of thetransmitter circuit and the monitoring receiver circuit will be zero dueto the fact that transmitter-conductor tl is connected in parallel withconductor 153 which parallel conductors neutralize and balance out thecapacity unbalance efiect of i2 on either of the conductors mrl or mrZ.For example, if we assume at any instant a positive potential onconductor t2 an equal negative potential will be present on bothconductors ti and t3 which obviously will neutralize the effect oneither conductor mrl or mrl of the positive potential of t2.

In normal practice, the positive side of the operators telephone circuitbattery B, Fig. l is grounded and therefore conductor IE2 is grounded atone end and a more effective and stable shield between the two receivercircuits is therefore provided if the same conductor, t2, is alsogrounded at the other end of the cord, as shown in the drawing.

What is claimed is:

1. In a telephone transmission system comprising a cable including twosets of two conductors each for separate transmission in the samedirection and a third set for transmission in the opposite direction,means for reducing crosstalk between said first two sets and betweensaid third set and either of the other two sets characterized in thisthat said individual sets of conductors lie in parallel equidistantplanes with the third set intermediate the other two, said third sethaving three conductors the outer two of which are connected together,and all of said seven conductors being so spaced with respect to eachother that a substantially uniform capacity exists between eachconductor of the first two sets and its two adjacent conductors of thethird set.

2. In a telephone transmission system comprising a cable including twosets of conductors each for separate transmission in the same directionand a third set for transmission in the opposite direction, means forreducing crosstalk between said first two sets and between said thirdset and either of the other two sets characterized in this that theconductors of said in dividual sets lie closely adjacent each other indifferent parallel planes closely adjacent and equidistant from eachother, with the third set intermediate the other two and having threeconductors the outer two of which are connected together at each end ofthe cable.

3. In a telephone transmission system comprising a cable including sevenconductors arranged in three separate groups for providing threeindependent transmission circuits, means for reducing crosstalk betweensaid independent circuits characterized in this that the conductors ofeach circuit group lie closely adjacent to each other in closelyadjacent parallel planes, two of said circuits comprising two conductorseach and the third circuit comprising three conductors whose plane isintermediate the other two, and having its outer two conductorsconnected togather to form one conductor of a circuit pair.

4. In a telephone transmission system comprising a cable including sevenconductors arranged in three separate groups for providing threeindependent transmission circuits, means for reducing crosstalk betweensaid independent circuits characterized in this that the conductors ofeach circuit group lie closely adjacent to each other in closelyadjacent, parallel planes, two of said circuits comprising twoconductors each and the third circuit comprising three conductors whoseplane is intermediate the other two, the outer two of said threeconductors being connected together at each end of the cable, the thirdconductor of said three-conductor group being equidistant from the othersix conductors and each conductor of the two outer groups beingequidistant two of the conductors of the third group.

LANGFORD J. BOWNE.

